Adsorption of iodine on metal coupons in humid and dry environments

[摘要] In this study, five different metal coupons were evaluated for gaseous iodine [I-2(g)] adsorption including two stainless steels (i.e., SS304 and SS316), two Inconel alloys (i.e., 625 and 718) and pure Ni (i.e., Ni-200) within a dynamic flow-through system where temperature, iodine concentration, flow rate, atmosphere, and relative humidity were controlled. Humidity was shown to be critical to iodine adsorption on SS304, SS316, and Ni-20 0 at ambient temperatures. The results presented herein provide evidence that a moisture-mediated reaction is occurring. However, higher humidity levels decrease the adsorption, suggesting an ideal range of humidity for the highest corrosion potential in these metals. A comparison of the five metal substrates showed the highest I-2(g) adsorption in the following descending order: Ni-20 0 > SS304 > SS316 > 718 > 625. The Inconel 625 and 718 alloys were fairly inert to iodine adsorption under the conditions tested. Characterization of the coupons by scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction of the Ni-20 0 coupon indicates that NiI2 formed and flaked off the surface as a black powder. The SS304 and SS316 coupons showed evidence of extensive reactions with I-2(g) and formed a much more deliquescent corrosion product, which reacted with air when removed from the flow-through system for weighing on the analytical balance. A static system was also used to expose separate polished coupons to I-2(g), which allowed for analysis of the corrosion layers via scanning electron microscopy. These findings assisted in predicting iodine adsorption behaviors on a variety of metal surfaces under near-ambient conditions. (C) 2021 Elsevier B.V. All rights reserved.

[发布日期] 2021-12-01

[关键词] iodine capture;metal substrates;chemisorption